1. Field of the Invention
The present invention concerns planimeters. It has particular, although not exclusive, application to planimeters based on transmission of ultrasound or other radiation.
2. Background Information
Many applications arise in which lengths, areas, and other quantities need to be inferred from scale-model drawings of buildings, plots of land, mechanical devices, etc. Even when the drawing features are single straight lines, determining the length of the real-world feature thereby represented takes time. So planimeters have been developed to make that task easier. Planimeters usually comprise some kind of wheel that gets rolled along the drawing feature to be measured and infers the feature's length from the number of rotations. Some additionally have provisions for entering the drawing scale, and the output produced by the planimeter is the result of multiplying the measured length by the scale.
Some planimeters have pairs of wheels that, due to differences in the wheels' rotations, enable them to infer not only one-dimensional length but also relative directions. Such planimeters often calculate and produce derived quantities such as areas. So planimeters contribute greatly to the ease of determining from drawings quantities such as how much carpet a room requires or how long a fence it would take to enclose a yard.